1. Field of the Disclosure
The present disclosure relates to an organic light emitting diode device (hereinafter, will be referred to as “OLED” device), and particularly, to an OLED device capable of having an enhanced environment reliability by preventing moisture from being introduced thereinto from outside, and a method for fabricating the same.
2. Background of the Disclosure
An organic light-emitting diode (OLED) device, one of flat panel display devices, has high brightness and a low operation voltage. Further, the OLED device has a high contrast ratio because it is a spontaneous light-emitting type, and it can implement a display of an ultra thin thickness. The OLED device can easily implement moving images due to a short response time corresponding to several micro seconds (μs). Besides, the OLED device has no limitation in a viewing angle, and has a stable characteristic even at a low temperature. Further, as the OLED device is driven at a low voltage such as a direct current of 5-15 v, it is easy to fabricate and design driving circuits.
The OLED device can be fabricated in a very simple manner, because only deposition and encapsulation equipment is required.
The OLED device having such characteristics is largely categorized into a passive matrix type and an active matrix type. In the passive matrix type, scan lines and signal lines cross each other to form an OLED device in a matrix form. In order to drive each pixel, the scan lines are sequentially driven. Accordingly, for a required average brightness, an instantaneous brightness, a value obtained by multiplying an average brightness by the number of lines, should be implemented.
On the other hand, in the active matrix type, a thin film transistor (TFT), a switching device for turning on/off a pixel region, is located at each pixel region. A driving thin film transistor connected to the switching thin film transistor is connected to a power line and a light-emitting diode, and is formed at each pixel region.
A first electrode connected to the driving thin film transistor is turned on/off in unit of a pixel region, and a second electrode facing the first electrode serves as a common electrode. The first electrode, the second electrode, and an organic light-emitting layer interposed between the two electrodes constitute the light-emitting diode.
In such active matrix type, a voltage applied to a pixel region is charged in a storage capacitor (Cst). Power should be applied to the OLED device until a subsequent frame signal is applied to the OLED device. Under such configuration, the OLED device is continuously driven for a single frame, regardless of the number of scan lines.
Even if a low current is applied to the OLED device, the same brightness is implemented. Owing to characteristics of low power consumption, high resolution and a large screen, the active matrix type is being spotlighted in recent years.
A basic structure and an operation characteristic of such active matrix type OLED device will be explained with reference to the attached drawings.
FIG. 1 is a circuit diagram illustrating a configuration of a single pixel region of an active matrix type OLED device in accordance with the conventional art.
Referring to FIG. 1, a single pixel region of an active matrix type OLED device is composed of a switching thin film transistor (STr), a driving thin film transistor (DTr), a storage capacitor (Cst) and a light-emitting diode (E).
Gate lines (GL) are formed in a first direction, and data lines (DL) are formed in a second direction perpendicular to the first direction, thereby defining pixel regions (P). A power line (PL) for applying a power voltage to the OLED device is spaced from the data line (DL).
A switching thin film transistor (STr) is formed at an intersection between the data line (DL) and the gate line (GL), and a driving thin film transistor (DTr) electrically connected to the switching thin film transistor (STr) is formed in each pixel region (P).
The DTr is electrically connected to a light-emitting diode (E). More specifically, a first electrode, a terminal disposed at one side of the light-emitting diode (E) is connected to a drain electrode of the DTr. A second electrode, a terminal disposed at another side of the light-emitting diode (E) is connected to a power line (PL). The power line (PL) transmits a power voltage to the light-emitting diode (E). A storage capacitor (Cst) is formed between a gate electrode and a source electrode of the DTr.
Once a signal is applied to the OLED device through the gate lines (GL), the STr is turned on. And the DTr is turned on as a signal of the data lines (DL) is transmitted to the gate electrode thereof. Accordingly, light is emitted through the light-emitting diode (E). If the DTr is turned on, a level of a current applied to the light-emitting diode (E) from the power line (PL) is determined. As a result, the light-emitting diode (E) can implement a gray scale.
The storage capacitor (Cst) serves to maintain a gate voltage of the DTr constantly when the STr is turned off. Accordingly, even if the STr is turned off, a level of a current applied to the light-emitting diode (E) can be constantly maintained for the next frame.
FIG. 2 is a sectional view schematically illustrating an OLED device in accordance with the conventional art.
Referring to FIG. 2, in the conventional OLED device 10, an active area (AA, display region) and a non-active area (NA, non-display region) formed outside the active area (AA) are defined on a substrate 11. A plurality of pixel regions (P) defined by gate lines (not shown) and data lines (not shown) are formed at the active area (AA). A power line (not shown) is formed in parallel to the data lines (not shown).
A switching thin film transistor (not shown) and a driving thin film transistor (DTr) are formed at each pixel region (P).
In the conventional organic light-emitting diode device 10, the substrate 11, where the DTr and the light-emitting diode (E) have been formed, is encapsulated by a barrier film (not shown).
The conventional OLED device 10 will be explained in more detail. As shown in FIG. 2, an active area (AA) and a non-active area (NA) formed outside the active area (AA) are defined on a substrate 11. A plurality of pixel regions (P) defined by gate lines (not shown) and data lines (not shown) are formed at the active area (AA). A power line (not shown) is formed in parallel to the data lines (not shown).
A plurality of driving circuit lines (GIP), ground lines (GND), etc. are formed in the non-active area (NA) of the substrate 11.
Although not shown, the DTr is composed of a semiconductor layer, a gate insulating layer, a gate electrode formed on the gate insulating layer on the semiconductor layer, a source electrode and a drain electrode. The source electrode and the drain electrode are formed on an interlayer insulating layer formed on the gate insulating layer including the gate electrode, and are spaced from each other.
An interlayer insulating layer 13 having a drain contact hole (not shown) through which a drain electrode (not shown) of the DTr is exposed to outside, and an organic planarization layer 15 are formed on the DTr and the switching thin film transistor (not shown).
A first electrode 19, contacting the drain electrode (not shown) of the DTr through the drain contact hole (not shown) and provided for each pixel region (P) in a separated manner, is formed on the organic planarization layer 15.
A bank 212, by which the pixel regions (P) are separated from each other, is formed on the first electrode 19. The bank 21 is disposed between the pixel regions (P) adjacent to each other. The bank 21 is also formed in the non-active area (NA), i.e., at an outer portion of a panel.
An organic light-emitting layer 23, composed of organic light-emitting patterns (not shown) which emit red, green and blue light, is formed on the first electrode 19 in each pixel (P) enclosed by the bank 21.
A second electrode 25, a cathode is formed on the organic light-emitting layer 23 and the bank 21, in both of the active area (AA) and the non-active area (NA). The first electrode 19, the second electrode 25, and the organic light-emitting layer 23 interposed between the two electrodes 19, 25 constitute a light-emitting diode (E).
A first passivation layer 27, an insulating layer for preventing introduction of moisture into the OLED device 10, is formed on the entire surface of the substrate 11 including the second electrode 25.
An organic layer 29, formed of an organic material such as a polymer, is formed on the first passivation layer 27 at the active area (AA).
A second passivation layer 31, configured to prevent introduction of moisture into the OLED device 10 through the organic layer 29, is further formed over the first passivation layer 27 including the organic layer 29.
A barrier film (not shown) is positioned on the entire surface of the substrate including the second passivation layer 31 in a facing manner, for encapsulation of the light-emitting diode (E) and for prevention of introduction of moisture from the upper side. An adhesive (not shown, will be referred to as ‘Press Sensitive Adhesive’, PSA) is interposed between the substrate 11 and the barrier film (not shown), so that the substrate 11 and the barrier film can be completely attached to each other without an air layer therebetween. The second passivation layer 31, the adhesive (not shown) and the barrier film (not shown) have a face seal structure.
As the substrate 11 and the barrier film (not shown) are attached to each other by the adhesive (not shown) to thus form a panel, the OLED device 10 according to the conventional art is implemented.
However, the conventional OLED device may have the following problems.
Firstly, when a defect occurs in the face seal structure, e.g., the barrier film, the adhesive, etc., moisture (H2O) is rapidly introduced into an active area (AA) through a planarization layer. In order to solve such problem, a planarization layer may not be formed at a non-active area (NA). However, in this case, an inorganic insulating layer such as the passivation layer disposed on the OLED device has a degraded quality due to a stair-shaped portion.
Secondly, when a defect occurs in the face seal structure, e.g., the barrier film, the adhesive, etc., moisture (H2O) is rapidly introduced into the active area (AA) through a bank. In order to solve such problem, a bank may not be formed in the non-active area (NA). However, in this case, moisture may spread through a planarization layer to cause a problem.